Question:medium

Regular polygons A and B have number of sides in the ratio \(1:2\) and interior angles in the ratio \(3:4\).Then the number of sides of B equals

Updated On: Jan 15, 2026
Show Solution

Correct Answer: 10

Solution and Explanation

The objective is to determine the number of sides of two regular polygons, A and B, given that the ratio of their interior angles is 3:4. The process is divided into sequential steps:

Step 1: Variable Definition

Let n represent the number of sides of polygon A. Consequently, polygon B will have 2n sides, reflecting a 1:2 ratio in the number of sides.

Step 2: Interior Angle Formula

The formula for the sum of interior angles in a polygon with n sides is:

\(\text{Sum of interior angles} = (n - 2) \times 180^\circ\)

For a regular polygon, the measure of each interior angle is calculated as:

\(\text{Each interior angle} = \frac{(n - 2) \times 180}{n}\)

Step 3: Interior Angle Ratio Setup

The provided ratio of interior angles between polygons A and B is 3:4. This translates to the following equation:

\(\frac{ \frac{(n - 2) \times 180}{n} }{ \frac{(2n - 2) \times 180}{2n} } = \frac{3}{4}\)

Step 4: Equation Simplification

The equation is simplified as follows:

\(\frac{ (n - 2) \times 180 }{ n } \times \frac{ 2n }{ (2n - 2) \times 180 } = \frac{3}{4}\)

Further simplification yields:

\(\frac{ (n - 2) \times 2n }{ n \times (2n - 2) } = \frac{3}{4}\)

After canceling common factors and simplifying:

\(\frac{ 2(n - 2) }{ 2n - 2 } = \frac{3}{4}\)

Step 5: Solving for n

The value of n is found through cross-multiplication:

\(4 \times 2(n - 2) = 3 \times (2n - 2)\)

Expanding both sides results in:

\(8(n - 2) = 6n - 6\)

The simplified form is:

\(8n - 16 = 6n - 6\)

Rearranging terms to group n values:

\(8n - 6n = -6 + 16\)

\(2n = 10\)

Dividing by 2 gives the solution for n:

\(n = 5\)

Step 6: Calculating Sides for Polygon B

Since polygon B has 2n sides, the calculation is:

\(2 \times 5 = 10\)

Conclusion

Polygon A possesses 5 sides, and polygon B has 10 sides.

Was this answer helpful?
0


Questions Asked in CAT exam